High flow sensors generally use a bypass flow channel in combination with a main flow channel. A laminar flow element (LFE) may be incorporated in the main flow channel. A typical LFE may include multiple parallel flow channels with relatively small cross-sectional area to laminarize the main flow and create a pressure restriction. The bypass flow channel incorporates a means of sensing bypass flow and is fluidly communicated to the main flow channel via taps that are disposed perpendicular to the main flow channel. The taps may include a first tap and a second tap, with the first tap disposed upstream of the LFE and the second tap disposed downstream of the LFE.
The perpendicular orientation of the taps presents static pressure at the taps. The difference in the static pressure between the first and second taps drives flow through the bypass flow channel. The flowrate through the bypass flow channel may be controlled by features of the bypass, such as length and diameter, or an orifice or tube shaped feature may be used to limit bypass flow rate.
A relatively long bypass flow channel is desirable to reduce orifice effects that can be caused by differences in relationship of cross sectional area of the bypass channel to partitions in the laminar flow element. It is also desirable to implement this type of flow sensor with minimal size. It is further desirable to implement a flow sensor with variable length bypass flow channels. These three desires interact with one another.
Hence, there is a need for a flow sensor that addresses the above-noted enhancements. Specifically, one that has a relatively long bypass flow channel and/or a variable length bypass flow channel and/or can be implemented with minimal size. The present invention addresses at least these needs.